To achieve a circumferential arthrodesis (fusion) the anterior and the posterior columns must be treated. The goal of the treatment is the restoration of the lordotic curve and the anatomically correct disc space. Anteriorly, i.e. in the intervertebral space, implants like cages are inserted after disc removal. The posterior vertebral column, where the articular facet is located, should be locked as well. State-of-the-art techniques consider translaminar screws or transpedical instrumentation which, however, are not satisfactory.
Translaminar screws have certain disadvantages, like a) the screw insertion point is difficult to localize; the localization is done under full view, i.e. a separate posterior incision is performed medially whereas muscles must be separated from spinal and laminar processes. Most morbidity results from medial incision; b) the surgeon's view is two-dimensional due to the small incision which may result in interference of the second screw with the first one; and c) aiming devices or navigation tools did not improve insertion technique or precision of screw placement.
From U.S. Pat. No. 2001/007074 A1 STROBEL a bone screw is known.
From U.S. Pat. No. 4,754,749 TSOU another bone screw is known which has two closed canals in the screw head at an angle with the screw axis. A guide pin is insertable in one of these dosed canals, so that upon insertion of the guide pin it projects radially over the shaft and axially over the head of the screw which renders it complicated and rather unstable.
The invention as claimed aims at solving the above described problems.